cliff

an ambulance at the bottom of a cliff

Something that is helpful only after one is already injured or in trouble. The idea is that, while an ambulance at the bottom of a cliff can help people who fall off the cliff, a fence at the top would be more beneficial. Services like this, which only help kids once they've gotten into significant trouble, are like an ambulance at the bottom of a cliff.
See also: ambulance, bottom, cliff, of

cliffhanger

1. An ending of a piece of fiction (e.g., a television episode, chapter of a book, a film, etc.) characterized by a dramatically suspenseful and uncertain end. A good summer book always has a cliffhanger at the end of each chapter so that you never want to put it down! Judging by that movie's cliffhanger, I'd say we'll be seeing a sequel coming out fairly soon.
2. A serial television or film production characterized by such endings. That show is a cliffhanger—the episodes never really have endings.
3. Any contest, competition, or other such situation in which the outcome is suspenseful and uncertain until the very end. The two teams have been neck and neck for the entire second half, and with two minutes left this match has become a real cliffhanger. This election is looking like a cliffhanger, and we won't be able to truly say who's won until all the votes are counted.
Farlex Dictionary of Idioms.

cliff-hanger

A situation whose outcome is in extremely suspenseful doubt until the last moment. The term comes from serialized adventure films popular in the United States in the 1920s and 1930s, in which, at the end of each installment, the hero or heroine is left in a very dangerous situation, sometimes literally dangling from a cliff. The rationale, of course, was to entice the audience to return for the next installment in order to see what happened. By the 1940s the term was being transferred to other suspenseful states of affairs—for example, “the election was a cliff-hanger.”
The Dictionary of Clichés by Christine Ammer
See also:
  • an ambulance at the bottom of a cliff
  • dispatch (someone or something) from (some place)
  • dispatch from
  • do (someone or oneself) no favors
  • do somebody no favours
  • draw upon (someone or something)
  • stay away
  • stay away (from someone or something)
  • remain away
  • remain away (from someone or something)
References in classic literature
However, there was nothing else to consider than an attempt to scale the trees contiguous to the cliff in an effort to reach the caves above.
The Thark grasped the possibilities and the difficulties of the plan at once, but there was no alternative, and so we set out rapidly for the trees nearest the cliff.
The Gods of Mars
"I also have a life-saving mortar with which we might be able to throw a line over the summit of the cliffs; but this plan would necessitate one of us climbing to the top with the chances more than even that the line would cut at the summit, or the hooks at the upper end would slip.
"You see now," remarked Billings as we craned our necks to scan the summit thousands of feet above us, "how futile it would have been to waste our time in working out details of a plan to surmount those." And he jerked his thumb toward the cliffs. "It would take weeks, possibly months, to construct a ladder to the top.
The People That Time Forgot
Away beyond it rose a line of giant cliffs similar to those upon which we are supposed to stand in our survey of the savage scene, and through which the road had some how made its climb to the summit.
A Horseman in the Sky
Before us spread the Sojar Az, and else-where about us rose unscalable cliffs.
Pellucidar
He broke out through the smoke, stepping on a burning coal and screaming with the sudden hurt of it, and essayed to climb up the cliff. The arrows showered about him.
Before Adam
He was still three paces, however, from his victim's side when John upon the cliff above plucked up a huge boulder, and, poising it for an instant, dropped it with fatal aim upon the slinger beneath him.
The White Company
Cliffs, seemingly rising perpendicularly out of the sea, faded away into the mist upon either hand as we approached.
The Land That Time Forgot
And if Dowlas was to go and stand, and say he'd never seen a wink o' Cliff's Holiday all the night through, I'd back him; and if anybody said as Cliff's Holiday was certain sure, for all that, I'd back him too.
Silas Marner
That in some cases the sea, instead of spreading out sediment in a uniform sheet, heaps it round submarine rocks and islands, it is hardly possible to doubt, after examining the charts of the West Indies; and that the waves have power to form high and precipitous cliffs, even in land-locked harbours, I have noticed in many parts of South America.
The Voyage of the Beagle
The ground at the foot of the cliff was rocky and broken so that the going was slow and difficult.
The Lost World
The schooner paused not, but rushing across the harbour, pitched herself on that accumulation of sand and gravel washed by many tides and many storms into the southeast corner of the pier jutting under the East Cliff, known locally as Tate Hill Pier.
Dracula
To run seemed ridiculous, especially toward that steep and unscalable cliff, and yet I did so, and as I ran I saw Ja, agile as a monkey, crawl down the precipitous face of the rocks, clinging to small projections, and the tough creepers that had found root-hold here and there.
At the Earths Core
Its sources might lie among wild and inaccessible cliffs, and tumble and foam down rugged defiles and over craggy precipices; but its direction was in the true course, and up this stream he determined to prosecute his route to the Rocky Mountains.
Adventures of Captain Bonneville USA in the Rocky Mountains and